Why would people assume that? Why would people not already assume the forum approves them if they're posted here?
It's more like "support" than "approves." The forum would be held accountable since the forum "supports" this project with the fee that they paid which can be assumed as "agreement."I think paying some sort of fee is a good idea because most of these get rich quick schemesters/scammers only bother to make their crap coins because it costs absolutely nothing to them and then they even get free advertising with legions of shitposters. If they actually had to pay something I bet many wouldn't bother.
It won't stop them. Let's say there is a project made to scam others then in order for them to post it here then they pay 1 bitcoin then proceed. People would start investing then they can just run considering that they acquire more bitcoins which is far more greater than 1 bitcoin. Hence, even if the 1 bitcoin fee is implemented then there will be not much of a chang but rather for the forum's administration to get richer. 
